1. Field of the Invention
The invention relates to a method for producing a workpiece with centering regions or centers for machining between centers, said workpiece being produced from an elongated blank or intermediate product, as well as to a workpiece with corresponding centering regions.
2. Related Technology
It is known from the prior art to clamp elongated components for machining between centers in order to be able to machine said components over the entire surface, in particular when machining in lathes, in order to avoid machining defects or in order to make it possible to machine/turn in both directions. To this end, centers are provided in the workpiece to be machined at two oppositely situated (when viewed in the longitudinal direction of the workpiece) (end) faces; preferably cone-shaped centers. A driven tip of a lathe is introduced into the center on one side of the workpiece and an entrained tip of a lathe is introduced into the oppositely situated center and the workpiece is clamped at its oppositely situated (end) faces in this manner. On the machine side, the driven tip is clamped in the operating spindle of the lathe, whilst the entrained tip is clamped in the tailstock of the same.
During machining (turning, grinding etc.) between centers, it is necessary for the length tolerance between the contact faces of the centers or other types of centering regions to be as small as possible in order to make uniform finishing possible over several workpieces. Thus, for example, when providing toothing in a workpiece by means of machining between centers, the toothing can extend too far or not far enough in the longitudinal direction of the workpiece and can consequently impair other geometric contours of the workpiece or the region of the engagement of the toothing.
In addition, for the purchaser of prefabricated workpieces (for example blanks for constant velocity drive shafts) who wants to machine them further or finish them by machining between centers, it is, as a rule, very time-consuming and very costly to provide centers subsequently in the workpiece, for example through metal-cutting methods such as drilling.
On the part of the supplier and manufacturer of the prefabricated workpiece, the centers are generally able to be introduced at the same time directly during the manufacture of the workpiece. For example, when workpieces are produced by means of cold-forging, warm-forging or hot-forging (e.g. hot extrusion), length tolerances of the workpiece of approximately +/−2 mm are achieved. In the case of the workpiece produced by forging a blank or intermediate product, this means that during forging centers that were introduced at the same time—or better the actual measurement of the distance between the contact faces of the centers or other types of centering regions for the machining between centers—also lie in a high tolerance range, it only being possible to achieve minimum tolerances of +/−0.6 to +/−0.8 mm. If a workpiece of this type is further machined on the part of the purchaser, the tolerance per workpiece has to be determined individually in order to balance it out during machining. This, in turn, requires a high amount of expenditure of measuring and subsequently an individual adjustment of the machine for each workpiece, which means a high level of expenditure of time and money and makes automatic production almost impossible; at best in the case of workpieces with small tolerance defaults.
As an alternative to this, it is also possible, in a further method step, to compress the entire workpiece after production thereof and after the introduction of centers, however, as a rule, before further machine-cutting, which requires a high level of expenditure on labor, energy and costs. In addition, the compressing impairs the geometry of the workpiece over the entire workpiece length, which increases the risk of scrap.